76 Lord Kelvin on the Age of the 



account, and Mr. Clarence King, after a careful scrutiny of 

 all the data given him for this purpose by Dr. Barus, concludes 

 that without further experimental data " we have no warrant 

 for extending the earth's age beyond 24 millions of years." 



§ 19. By an elaborate piece of mathematical book-keeping 

 1 have worked out the problem of the conduction of heat 

 outwards from the earth, with specific heat increasing up to 

 the melting-point as found by Riicker and Roberts-Austen 

 and by Barus, but with the conductivity assumed constant ; 

 and, by taking into account the augmentation of melting- 

 temperature with pressure in a somewhat more complete 

 manner than that adopted by Mr. Clarence King, I am not 

 led to differ much from his estimate of 24 million years. 

 But, until we know something more than we know at present 

 as to the probable diminution of thermal conductivity with 

 increasing temperature, which would shorten the time since 

 consolidation, it would be quite inadvisable to publish any 

 closer estimate. 



§ 20. All these reckonings of the history of underground 

 heat, the details of which I am sure you do not wish me to 

 put before you at present, are founded on the very sure 

 assumption that the material of our present solid earth all 

 round its surface was at one time a white hot liquid. The 

 earth is at present losing heat from its surface all round from 

 year to year and century to century. We may dismiss as 

 utterly untenable any supposition such as that a few thousand 

 or a few million years of the present regime in this respect 

 was preceded by a few thousand or a few million years of 

 heating from without. History, guided by science, is bound 

 to find, if possible, an antecedent condition preceding every 

 known state of affairs, whether of dead matter or of living 

 creatures. Unless the earth was created solid and hot out 

 of nothing, the regime of continued loss of heat must have 

 been preceded by molten matter all round the surface. 



§ 21. 1 have given strong reasons * for believing that 

 immediately before solidification at the surface, the interior 

 was solid close up to the surface : except comparatively small 

 portions of lava or melted rock among the solid masses of 

 denser solid rock which had sunk through the liquid, and 

 possibly a somewhat large space around the centre occupied 

 by platinum, gold, silver, lead, copper, iron, and other dense 

 metals, still remaining liquid under very high pressure. 



§ 22. I wish now to speak to you of depths below the 



* « On the Secular Cooling of the Earth," vol. iii. Math, and Phys. 

 Papers, §§ 19-33. 



